Preservation and processing of fish


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Preservation and processing of fish

  2. 2. How long can fish or meat be kept?  Fresh fish will spoil very quickly. Once the fish has been caught, spoilage progresses rapidly. In the areas of high temperature, fish will spoil within 12 hours, which make them unconsumable.  Thus the marketing of fish becomes difficult task because the fish should reach the consumer before the quality of fish reduces.
  3. 3. When has fish or meat gone bad?  Spoilage is the deterioration of food which make its taste and smell bad ( sour or rotten) and makes it a carrier of disease germs.  In fish and meat the most important kinds of spoilage are:  1. autolytic spoilage caused by enzymes  2 .microbiological spoilage caused by bacteria  3 .fat oxidation  Breakdown of proteins occur fastly in fish flesh as compared to other meat although the composition is same.
  4. 4. 1) Enzymic changes  Enzymes are proteins which assist biological reactions, e.g. the conversion of certain organic substances into different ones. When fish or animals are killed, the enzymes inside them are still intact.  Those enzymes start breaking down components into smaller parts and cause release of toxic substances, which affects smell, taste and makes the flesh soften.  Formation of TMA (trimethylamine), DMA and NH3 by decomposition causing deterioration producing bad smell.  PH increases from normal 6.4 to 7.8
  5. 5. 2) Bacterial spoilage  Bacteria are the micro organisms invisible to naked eye, break down the wastes and bodies of dead organisms.  Under favorable conditions and due to enzymatic changes microbiological spoilage starts quickly in fresh and non-acidic products such as fish and meat.  They breakdown the cellular part or matrix of flesh by secreting some enzymes.
  6. 6. 3) Fats Oxidation  With fatty fish or meat, chemical reactions can take place between the fat and oxygen in the air (oxidation reactions).  By exposing these products for a long time to air, e.g. during drying and smoking, the product acquires a rancid smell and taste.
  7. 7. Therefore preservation
  8. 8.  Preservation is the processing of food so that they can be stored for a longer time.  Preserved food is not healthy as fresh food because it decreases the nutrition value of food.  Before preservation, fish is processed and washed with clean water to remove the mucus and other such materials which can cause problem in preservation.
  9. 9. Methods of preservation  Fish can be preserved through  Drying  Freezing  Salting  Smoking  Canning
  10. 10. 1 1)---DRYING  Drying is the oldest way of preserving foods.  When sufficient water is removed from a product, micro-organisms can no longer grow.  The simplest and cheapest method is to dry the product in the open air (with or without sun).  They are hanged on ropes for two or three days with regular turning over of fishes in order to expose every part to the sun.
  11. 11. Drying
  12. 12. 2)--FREEZING  In this method the fishes are kept in wooden boxes from all sides or in freezing cells with a temperature of -20 to -30 degree centigrade.  The low temperature prevents bacterial action and autolysis.  The fish can be freezed for not more than 6 months after that quality of fish reduces.
  13. 13. 3) SALTING  Salt is the preservative agent used to lengthen the shelf life of fish and fishery products. This is used in almost all methods of preservation except in icing, refrigeration and freezing.
  14. 14. PROCESS  In this type of preservation salt is rubbed on all sides of fish including the visceral cavity.  On thicker parts of fish, scars are made by knife and then salt is rubbed there for deep penetration.  These fishes are kept in cemented or metallic tubs in layers , each layer having a thick coating of salt on both sides.  After about three days these fishes are removed and dried in sun for 2 to 3 days. This common salt inhibits the growth of micro organisms and makes the enzymes inactive.
  15. 15. Salting
  16. 16. 4)--SMOKING  Raw fish and meat can also be preserved by smoking. The preserving effect of the smoke is a result of drying (withdrawal of moisture) of the product during the smoking.  The smoke particles, after being absorbed by the product, inhibit bacterial growth on the surface of the product. 
  17. 17.  Preparation  Fish can be smoked whole, cleaned, split or filleted, depending on local preferences and the desired final product.  Meat must be cut into strips 5 cm wide and 1 cm thick before being smoked. An important fact is that the greater the surface area of the meat or fish, the greater the amount of smoke particles which can be absorbed during smoking and the better the product can dry.  Applying of salt solution and sun drying before smoking gives better result.
  18. 18. Smoking ovens
  19. 19. 19 5) Basics of Canning  Food is placed in a jar and heated to a temperature that destroys targeted microorganisms.  Heat also inactivates enzymes that cause spoilage.  Air is driven from the jar during heating. As the jar cools a vacuum seal is formed. Can It!
  20. 20. Steps to canning fish 1. Start with fresh and healthy fish. Remove the head, tail and bones of large fish and wash thoroughly with cold water. 2. Cut into desired size pieces. 3. The fish is also salted and smoked to remove blood and water from flesh, this also denatures the protein which makes the fish stay firm and not shrink after canning. 4. Fill hot, clean, pint or half-pint jar, leaving 1-inch headspace.  Seal jar and place in canner.  Process for 100 minutes at 240 degrees at11 pounds pressure with a dial gauge.
  21. 21. Continue….  Turn off heat at the end of processing.  Let pressure drop to 0 psig naturally.  Wait 2 minutes after pressure drops.  Open the canner.  Remove the jars and cool it for 24 hours undisturbed.
  22. 22. Pressure canning
  23. 23. THANKS